Button-type batteries are small, thin energy cells that are commonly used in watches and other electronic devices requiring a thin profile. A conventional button-type battery includes two electrodes in the form of an anode and a cathode. These are typically separated by a porous separator. An electrolyte is present within pores of the separator.
These internal battery components are housed within a metal casing or housing formed by a lower conductive can and an upper conductive lid. A common prior art material for the can and lid is stainless steel. The can is typically in electrical contact with the cathode to form the positive battery terminal, and the lid is in electrical contact with the anode to form the negative battery terminal. The can and lid are crimped or pressed together to form a fluid-tight seal which entirely encloses the anode, cathode, separator, and electrolyte. An electrically insulating sealing gasket is provided within the primary seal between the lid and can to electrically isolate the two housing members.
There is a need in button-type battery usage to make such energy cells thinner. Today, the thinnest commercially available button-type battery has a thickness of 1.2 mm (47.2 mils). It would be desirable to make a thinner battery, particularly one having a thickness of less than 1 mm (39.4 mils). A countering concern, however, is that the integrity of the fluid-tight seal cannot be compromised simply to achieve the goal of thinner batteries.
One challenge in the fabrication of thin button cells concerns the battery seal. Industry standard coin cell battery gaskets typically employ an injection molded polymer gasket (i.e., polypropylene or polyethylene). Minor imperfections and voids in the crimped gasket seal area are normally filled by the application of a supplemental sealant material, such as asphalt. However, conventional injection molding technology is not easily adapted to ultra-thin button cell batteries due to the minimum thickness of the gasket that can be cost effectively obtained. Further, water permeability of the seal becomes problematic with thinner and thinner button cell gaskets and seals.
Accordingly, needs remain in the development of improved materials and methods associated with button-type battery seals.